This invention relates to a process and apparatus for electrochemically refining spent nuclear fuel from a nuclear reactor and recovering purified uranium and a mixture of uranium and plutonium for use as fresh blanket and core fuel in a nuclear reactor. The invention relates to a electrorefiner of the type wherein spent blanket and core fuel is refined in a single electrorefining cell by transferring uranium and plutonium from the spent fuel optionally to a molten cadmium pool or directly to an electrolyte and thereafter electrolytically depositing purified uranium on a solid cathode and subsequentially electrolytically depositing a mixture of uranium and plutonium on a second liquid metal cathode, preferred cadmium.
Electrorefining processes have been generally used to recover high purity metal or metals from impure feed materials and more particularly to recover materials such as uranium and plutonium from spent nuclear fuel. Electrorefining of spent nuclear fuel is carried out in a electrolysis cell of the kind disclosed in U.S. Pat. Nos. 2,951,793, 4,596,647, 4,880,506, 4,855,030 and 5,009,752, the disclosures of each of these patents being incorporated herein by reference and are generally indicative of the prior art in this field.
In such cells as disclosed in the above-mentioned patents, the spent nuclear fuel forms the anode or is dissolved in an anode pool. An electrolytic fuel cell is used, and the purified metal is transferred electrolytically and collected on the cathode. In other designs, an anode pool is located at the bottom of the cell, and the cathode may be located above the anode in the electrolyte pool. It has been found in the prior art that relatively pure uranium can be electrolytically deposited on a solid cathode and thereafter mixtures of uranium and plutonium can be deposited on a molten metal cathode such as cadmium, see the above-identified U.S. Pat. No. 4,880,506. In all of the art cited above, and in the electrorefining process as it now exists, the anode is located no closer than about 9 inches to the cathode. This is the state of the art as it existed before the subject invention. It is understood that the electrical resistance of the cell is greatly influenced by the space between the anode and the cathode and the cell resistance is such that the limiting average electrical current is about 200 amperes in the current test cell at Argonne National Laboratory, for transport from the anode to the solid cathode for uranium collection and about 80 amperes for transfer to the liquid cathode such as cadmium for the collection of a combination of plutonium and uranium. Since the transport rate is directly proportional to cell current, decreasing the cell resistance increases the transport rate; otherwise, the preset voltage limit is reached earlier due to the higher resistance.